Introduction
Phytophthora botryosa Chee (1969)
Phytophthora botryosa was first isolated from leaf petioles of the rubber tree (Hevea brasiliensis) in Malaysia and Thailand and described by Chee in 1969. The pathogen causes leaf fall and pod rot of rubber trees (Chee, 1969; Chee and Wastie, 1980) and pod rot of cacao (Chee and Wastie, 1970) and has been reported on taro (Zheng and Lu, 1989). It is classified in group II by Stamps (1985) and Stamps et al. (1990) (Fig. 1).
Cultural Characteristics
Colonies are slow growing and slightly radiate with little aerial mycelium (Fig. 2). The minimum temperature for growth is 9°C, the optimum temperature for growth is 26°C, and the maximum temperature for growth is 32°C. There is no colony growth at 35°C or higher.
Reproductive Structures
Asexual Structures
Sporangiophores:
Sporangiophores
are sympodial.
Sporangia:
Sporangia
are
papillate
and spherical, ovoid, ellipsoidal, or obturbinate and are 20–51 × 28–69
µm (Fig. 3). Sporangia are caducous
with a medium
pedicel
length of 10–20 µm or less. Length–breadth ratios are 1.6–2.1. Sporangia
form in botryose clumps.
Chlamydospores:
Chlamydospores
are produced
infrequently (sparse) and are 14–30 µm (average 18.7 µm).
Sexual Structures
P. botryosa is
heterothallic
and produces
oospores
when paired with differing mating types (A1 and A2).
There are occasional
oospores
in single culture.
Antheridia:
Antheridia
are
amphigynous, spherical, and 8–12 × 12.5–21 µm.
Oogonia:
Oogonia
are smooth
walled, hyaline to yellow, and 21.7–31.7 µm (average 28 µm).
Oospores:
Oospores form abundantly in host tissues and have a diameter of 20.9–27.6 µm (average 25.1 µm) (Fig. 4).
Host Range and Distribution
Host |
Common Name |
Disease |
Geographical Distribution |
Hevea brasiliensis |
Rubber tree |
Green pod decay |
|
Colocasia esculenta |
Taro |
Root rot |
|
Theobroma cacao |
|
Pod rot |
|
Symptoms
Symptoms are similar to those of
P. meadii
on
Hevea spp. The pathogen attacks the fruit, leaves, bark, and
green shoots of the rubber tree. The
symptoms on the fruit include dullish gray spots that develop at the stem
end and spread across the entire fruit.
It causes leaf fall and branch dieback.
The pathogen can survive in bark cankers and causes a "stripe canker"
on the bark (Erwin and Ribeiro, 1996).
References
Chee, K. H. 1969. Variability of Phytophthora species from Hevea brasiliensis. Trans. Br. Mycol. Soc. 52:425-436.
Chee, K. H., and Wastie, R. L. 1970. Black pod disease of cacao. Planter,
Chee, K. H., and Wastie, R. L. 1980. The status and future prospects of
rubber diseases in tropical
Erwin, D. C., and Ribeiro, O. K. 1996. Phytophthora
Diseases Worldwide. American Phytopathological Society,
Stamps, D. J. 1985. Phytophthora botryosa. CMI Descr. Pathog. Fungi Bact. 835:1-2.
Stamps, D. J., Newhook, F. J., Waterhouse, G. M., and Hall, G. S. 1990.
Revised tabular key to the species of
Phytophthora
de Bary.
Mycol. Pap. 162.
CAB International, Wallingford, United Kingdom; Commonwealth Mycological
Institute, Kew,
Zheng, X. B., and Lu, J. Y. 1989. Studies on the
Phytophthora
species in